Two lean NO_x trap(LNT) catalysts, Pt/BaO/CeO_2 + Al_2O_3 and Pt/BaO/CeO_2-Al_2O_3, were prepared and compared for low-temperature(< 250℃) NO_x storage and reduction performance. The influence of the form of ceria...Two lean NO_x trap(LNT) catalysts, Pt/BaO/CeO_2 + Al_2O_3 and Pt/BaO/CeO_2-Al_2O_3, were prepared and compared for low-temperature(< 250℃) NO_x storage and reduction performance. The influence of the form of ceria on low-temperature NO_x storage and reduction performance of LNT catalysts was investigated with the focus on NO_x storage capacity, NO_x reduction efficiency during lean/rich cycling, product selectivity and thermal stability.Inductively coupled plasma-atomic emission spectrometry(ICP-AES), Brunner-Emmet-T eller(BET), H_2-pulse chemisorption and X-ray diffraction(XRD) were conducted to characterize the physical properties of LNT catalysts. NO_x storage capacity and NO_x conversion efficiency were measured to evaluate NO_x storage and reduction performance of LNT catalysts. Pt/BaO/CeO_2-Al_2O_3 catalyst exhibits higher NO_x storage capacity than Pt/BaO/CeO_2 + Al_2O_3 catalyst in the temperature range of 150-250 ℃. Meanwhile, Pt/BaO/CeO_2-Al_2O_3 catalyst shows better NO_x conversion efficiency and N_2 selectivity. XRD results indicate that the thermal stability of CeO_2-Al_2O_3 complex oxide is superior to that of pure CeO_2. H_2-pulse chemisorption results show that Pt/BaO/CeO_2-Al_2O_3 catalyst has higher Pt dispersion than Pt/BaO/CeO_2 + Al_2O_3 catalyst over fresh and aged samples. The improved physical properties of Pt/BaO/CeO_2-Al_2O_3 catalyst are attributed to enhance the NOx storage and reduction performance over Pt/BaO/CeO_2 + Al_2O_3 catalyst.展开更多
出于辐射防护目的,通常假定辐射诱发癌症的总危险是随着剂量呈线性无阈(Linear Non Threshold,LNT)增加。然而,现有流行病调查结果不能完全支持验证LNT,同时低剂量辐射生物效应研究发现了新的不利于LNT模型的成果,且现有的资料并不排除...出于辐射防护目的,通常假定辐射诱发癌症的总危险是随着剂量呈线性无阈(Linear Non Threshold,LNT)增加。然而,现有流行病调查结果不能完全支持验证LNT,同时低剂量辐射生物效应研究发现了新的不利于LNT模型的成果,且现有的资料并不排除有阈值存在,剂量响应关系的变化依赖于所论及癌症的类型、剂量、剂量率、辐射的传能线密度(Linear Energy Transfer,LET)、受照个体的年龄、性别和生理状态以及其他因素。尽管不排除其他剂量响应关系的存在,低水平辐射致癌效应的分析中没有其他模型比LNT模型更能被业界广泛接受。在新理论、新模型产生前,遵循现有理论和LNT模型评估辐射危害仍然是目前最科学的态度,同时也是最有利于辐射防护的方法论。展开更多
An experimental and model-based study of the effect of rich air/fuel ratios(AFRs) and temperature on the NOx slip of a lean NOx trap(LNT) was conducted in a lean-burn gasoline engine with an LNT after-treatment system...An experimental and model-based study of the effect of rich air/fuel ratios(AFRs) and temperature on the NOx slip of a lean NOx trap(LNT) was conducted in a lean-burn gasoline engine with an LNT after-treatment system. The emissions of the engine test bench and the inlet temperature of the LNT were used as the major inlet boundary conditions of the LNT. The engine periodically operated between a constant lean AFR of 23 with alterable rich AFRs of 10, 11, 12, 13, and 14. A decrease in the rich AFR of the engine strengthened the desorption atmosphere in the LNT, an effect closely related to the number of reductants, and further heightened the NOx desorption of the LNT, but with a penalty in fuel consumption. To eliminate that penalty, the inlet boundary conditions of the LNT were varied by adjusting the inlet temperature within a range between 200℃ and 400℃. An increase in inlet temperature heightened the NOx desorption of the LNT, and a NOx breakthrough occurred after the inlet temperature exceeded 390℃. To control NOx breakthrough, the inlet temperature can be adjusted to offset the strong desorption atmosphere in the LNT commonly created by a rich AFR.展开更多
基金financially supported by the National Key R&D Program of China (No. 2017YFC0211100)
文摘Two lean NO_x trap(LNT) catalysts, Pt/BaO/CeO_2 + Al_2O_3 and Pt/BaO/CeO_2-Al_2O_3, were prepared and compared for low-temperature(< 250℃) NO_x storage and reduction performance. The influence of the form of ceria on low-temperature NO_x storage and reduction performance of LNT catalysts was investigated with the focus on NO_x storage capacity, NO_x reduction efficiency during lean/rich cycling, product selectivity and thermal stability.Inductively coupled plasma-atomic emission spectrometry(ICP-AES), Brunner-Emmet-T eller(BET), H_2-pulse chemisorption and X-ray diffraction(XRD) were conducted to characterize the physical properties of LNT catalysts. NO_x storage capacity and NO_x conversion efficiency were measured to evaluate NO_x storage and reduction performance of LNT catalysts. Pt/BaO/CeO_2-Al_2O_3 catalyst exhibits higher NO_x storage capacity than Pt/BaO/CeO_2 + Al_2O_3 catalyst in the temperature range of 150-250 ℃. Meanwhile, Pt/BaO/CeO_2-Al_2O_3 catalyst shows better NO_x conversion efficiency and N_2 selectivity. XRD results indicate that the thermal stability of CeO_2-Al_2O_3 complex oxide is superior to that of pure CeO_2. H_2-pulse chemisorption results show that Pt/BaO/CeO_2-Al_2O_3 catalyst has higher Pt dispersion than Pt/BaO/CeO_2 + Al_2O_3 catalyst over fresh and aged samples. The improved physical properties of Pt/BaO/CeO_2-Al_2O_3 catalyst are attributed to enhance the NOx storage and reduction performance over Pt/BaO/CeO_2 + Al_2O_3 catalyst.
文摘出于辐射防护目的,通常假定辐射诱发癌症的总危险是随着剂量呈线性无阈(Linear Non Threshold,LNT)增加。然而,现有流行病调查结果不能完全支持验证LNT,同时低剂量辐射生物效应研究发现了新的不利于LNT模型的成果,且现有的资料并不排除有阈值存在,剂量响应关系的变化依赖于所论及癌症的类型、剂量、剂量率、辐射的传能线密度(Linear Energy Transfer,LET)、受照个体的年龄、性别和生理状态以及其他因素。尽管不排除其他剂量响应关系的存在,低水平辐射致癌效应的分析中没有其他模型比LNT模型更能被业界广泛接受。在新理论、新模型产生前,遵循现有理论和LNT模型评估辐射危害仍然是目前最科学的态度,同时也是最有利于辐射防护的方法论。
基金Project supported by the National Natural Science Foundation of China(Nos.50276042,50776062,and 51276128)the National High Technology R&D Program (863) of China(No.2008AA06Z322)the Tianjin Research Program of Application Foundation and Advanced Technology(No.11JCZDJC23200),China
文摘An experimental and model-based study of the effect of rich air/fuel ratios(AFRs) and temperature on the NOx slip of a lean NOx trap(LNT) was conducted in a lean-burn gasoline engine with an LNT after-treatment system. The emissions of the engine test bench and the inlet temperature of the LNT were used as the major inlet boundary conditions of the LNT. The engine periodically operated between a constant lean AFR of 23 with alterable rich AFRs of 10, 11, 12, 13, and 14. A decrease in the rich AFR of the engine strengthened the desorption atmosphere in the LNT, an effect closely related to the number of reductants, and further heightened the NOx desorption of the LNT, but with a penalty in fuel consumption. To eliminate that penalty, the inlet boundary conditions of the LNT were varied by adjusting the inlet temperature within a range between 200℃ and 400℃. An increase in inlet temperature heightened the NOx desorption of the LNT, and a NOx breakthrough occurred after the inlet temperature exceeded 390℃. To control NOx breakthrough, the inlet temperature can be adjusted to offset the strong desorption atmosphere in the LNT commonly created by a rich AFR.
